Automatic voltage regulator



Feb. 20, 1968 A. SENETCEN 3,370,223

AUTOMAT I C VOLTAGE REGULATOR Filed Nov. 27, 1964 v INVENTOR.

AZex 5enefc6/2 United States Patent Office 3,370,223 Patented Feb. 20, 1968 3,370,223 AUTOMATIC VOLTAGE REGULATOR Alex Senetcen, Forestville, Conn., assignor to The Superior Electric Company, Bristol, Conn., a corporation of Connecticut Filed Nov. 27, 1964, Ser. No. 414,363 5 Claims. (Cl. 323-22) ABSTRACT OF THE DISCLOSURE An automatic AC. voltage regulator for maintaining a substantially constant value of an output voltage in which the value of the output voltage is sensed and a signal related to the value of the output voltage is used to control the value of the impedance of a shunt path connected across the input terminals by varying the conductivity of semiconductors in the path.

While many types of regulators have heretofore been proposed, the regulator disclosed herein relates to the type in which there is apotential dividing network positioned across the input terminals of the regulator. The network may consist of a transformer means, such as an autotransformer, as one element and an adjustable impedance as the other element. The latter is connected to the transformer means to form a shunt path across the input terminals. By decreasing the impedance of the adjustable impedance, a greater voltage is made to appear across the transformer means and this increased voltage is reflected as an increase in the output voltage. Accordingly by controlling the impedance of the adjustable impedance shunt path with proper circuits that sense the value, the output voltage value may be maintained within a relatively small range. v

In heretofore known devices one form of an adjustable impedance has been a magnetic amplifier or saturable reactor with a controlling current determined by the variation of the output voltage from a selected value being utilized .to control the impedance to shunt path current through the load windings of the saturable reactor. While such devices have been operable, it has been found that cient and more economical than heretofore proposed devices.

Another object of the present invention is to provide an automatic voltage regulator of the shunt path type that is capable of reacting to return the value of output voltage to its desired value when it deviates therefrom in an extremely short time.

A further object of the present invention is to provide an adjustable voltage regulator which achieves the above objects by utilizing an adjustable impedance in which the control of the adjustable impedance requires only relatively simple and efiicient circuits and yet produces a regulator which is durable in use, provides a satisfactory,

distortion minimized output voltage and is relatively economical to manufacture.

' In the automatic voltage regulator of the present invention thereis provided a pair of input terminals and a pair of output terminals with the input terminals being connectible to a source of alternating current and the output terminals being connectible to a load to which it is desired to maintain a voltage substantially constant. The regulating unit for regulating the input voltage to the desired value of output voltage includes an autotransformer having an intermediate tap connected to one input terminal, with one end of the autotr-ansformer being connected to an output terminal and the other end being connected-to an adjustable impedance. The impedance is connected to the other input terminal which is made common with the other output terminal.

The adjustable impedance is thus electrically connected between the input terminals to form a shunt path. In the present invention the impedance consists of semiconductor means and specifically as it is desired to provide full wave control of the alternating current, of a pair of parallel inversely connected controlled rectifiers. The rectifiers either present a substantially infinite impedance or substantially a short-circuited path for current therethrough. For controlling the duration of each half cycle when the semiconductor means is rendered conducting, there is provided a measuring unit which senses the value of output voltage and provides a signal for rendering the semiconductor means conducting.

Other features and advantages will hereinafter appear.

In the drawings:

The figure is an electrical schematic diagram of the automatic voltage regulator of the present invention.

Referring to the drawing, the automatic voltage regulator of the present invention is generally indicated by the reference numeral 10 and includes a pair of input terminals 11 and 12 connectible to a source of alternating current and a pair of output terminals 13 and 14 connectible to a load, not shown, to which it is desired to provide a voltage that is maintained substantially constant. The regulating unit includes an autotransformer 15 having a tap 16 connected tothe input terminal 12, and end 17 connected to the output terminal 13 and another end 18. The end 18 is connected to the input terminal 11 through a pair of parallel but inversely connected controlled rectifier elements 19 and 20 with a series inductor 21 connected therebetween. Connected between the end 18 and the end 17 of the autotransformer 15 is a pair of filters 22 and 23 for the third and fifth harmonic of the alternating current frequency and if desired additional filters for other frequencies may be employed and in other and different connections to minimize the distortion of the output voltage wave form. There is also provided an inductance 24 connected between the output terminals 13 and 14 that effects a small bleed current across the output terminals for maintaining the operation of the regulator during times when the terminals 13 and 14 may not be connected to a load and thus be open circuited. The inductance 24 provides at .all times during open circuit conditions for the desired value of output voltage to appear across the terminals 13 and 14.

With the above structure of the regulating means, it will be appreciated that for the portion of each half cycle when a controlled rectifier is conducting, an increased voltage appears at the output terminals 13 and 14 by reason of the voltageat the end 18 of the transformerapproaching the voltage at the terminal 11. For the portions of each half cycle when a controlled rectifier is not conducting, then the voltage at the end 18 is greater than the voltage at the point 11, thuslowering the voltage across the autotransformer which makes a decreased voltage appear at the output terminals. Accordingly by varying the duration of each half cycle when a controlled rectifier is conducting, the average voltage value of the half cycle at the output terminals 13 and 14 may accordingly be maintained at a desired value. p

The measuring unit, generally indicated by the reference numeral 25, serves to apply through a pulse transformer 26 the proper signal to the gate and cathode of each controlled rectifier. The pulse transformer 26 includes a first secondary winding 27 having points E and F connected to the gate and anode of controlled rectifier 20 which have the same letters, a second secondary winding 28 having points C and D connected to the gate and cathode of controlled rectifier 19 which have the same letters, and a primary winding 29. Accordingly, whenever a voltage pulse or signal appears in the primary winding 29, it is transferred to both controlled rectifiers 19 and 20 with only the controlled rectifier having its anode and cathode properly polarized becoming conducting.

A unijunction transistor 30 has a base connected to one end of the primary winding 29 while the other end of the winding is connected to a lead 31 that is in turn connected to the minus side of a negative source of direct current, which may be minus 20 volts, with a lead 32 being connected to the positive side thereof. The emitter of unijunction transistor 30 is connected to a resistance capacitance network that includes a condenser 33, with the resistance being formed by a circuit that includes a resistor 34, a transistor 35 and a resistance 36. The latter resistance is positioned between the lead 31 and the emitter'of the transistor 35. It will be appreciated that the resistances 36, 34 and transistor 35 together with the condenser 33 from an RC network for the unijunction transisfor 30 and thus by varying the conduction of the transistor 35 in its emitter collector path, the time during each half cycle at which the voltage across the condenser 33 is sufficient to cause conduction through the emitter-base of the unijunction transistor 30 may accordingly be selected.

The transistor 35 is normally maintained conducting and the extent of conduction is determined by a resistance bridge 37 having in one leg a photoconductive cell 38. An incandescent lamp 39 is connected across a portion of a secondary 40 of a transformer 41 with the primary 42 thereof being connected across the output terminals 13 and 14 by the points having the same letters being connected together. A lead 43 is connected to the positive side of a direct current source while a lead 44 is connected to the negative side, with the source having a value of perhaps seventy volts. The values of resistances in the bridge 37 are set to provide the desired output voltage at the output terminals 13 and 14 by varying the voltage on the base of the transistor 35.

If the value of output voltage decreases below the selected value then the light emitted from the bulb 39 decreases, increasing the resistance of photocell 38 which in turn increases the negative bias between the emitter and base of transistor 35 causing it to conduct more. As it conducts more, the condenser 33 becomes charged sooner in the half cycle with a voltage that is suflicient to cause the unijunction transistor 30 to conduct, supplying a pulse to the primary winding 29 which is applied to the gatecathodes of the controlled rectifiers causing longer condnction thereof during the half cycle. This in turn will cause the value of output voltage at the terminals 13 and 14 to increase. Similarly, if the value of output voltage across the terminals 13 and 14 is higher than the selected value, the photocell 38 has a lesser resistance, the transistor 35 conducts less and the unijunction transistor 30 conducts later in the half cycle with a consequent lessening of the conduction of controlled rectifiers 19 and 20 for each half cycle. The value of output voltage Will thus be decreased to the selected value.

For assuring the discharge of the condenser 30 at the zero crossing of each half cycle, there is provided a transistor 45 which is rendered conducting for a short time after the zero crossing to decrease the voltage across the two bases of the unijunction transistor 30 to a very low value. As the unijunction transistor will conduct between its emitter and base whenever the emitter voltage is a fraction of the voltage across the two bases by reducing the base voltage to a small minimum, then the voltage across the condenser 33 may be made to discharge to the fraction of this minimum through the emitter-base of the unijunction transistor. The transistor has its base and emitter connected to opposite direct current junctions of a full wave rectifying bridge 46 while the other two junctions of the bridge are connected across the anodes and cathodes of the controlled rectifiers 19 and 20 which in effect places them at least, for the purposes of the transistor 45, across the input terminals 11 and 12.

Initially the leads 32 and 31 provide a voltage through a resistor 47 that biases the base-emitter of the transistor 45 to cause a conduction through the emitter collector thereof. As the alternating current increases from its instantaneous zero value an increasing value of voltage appears. across the positive junction 48 and negative junction 49 of the bridge 46 that is conducted through a circuit that includes a diode 50 which is connected between the emitter and base of transistor 45. As soon as the direct current voltage reaches a value sufficient to force current through the diode 50, the forward voltage drop across the diode appears across the emitter and base of the transistor 45. The voltage drop, which may be about one volt, has a value which is suflicient to reversely bias the emitter and base and consequently prevent conduction between the collector and emitter of the transistor 45. This enables the voltage between the leads 32 and 31 to be placed across the twobases of the unijunction transistor 30 thereby enabling it to be in condition to conduct when the value of voltage across the condenser 33 reaches the proper value.

When the transistor 30 conducts, and accordingly the controlled rectifiers 19 and 20, the voltage drop across the controlled rectifiers may or may not be sufficient to prevent conduction of the transistor 45 but in either event it is immaterial as the controlled rectifiers are maintained conducting inherently after conduction of the unijunction transistor 30 and the transistor 45 will stop conducting slightly after the zero crossing of each half cycle. While the transistor 45 is conducting, it will be appreciated that the condenser 33 is substantially discharged to zero and will be maintained this way until shortly after the zero crossing for each half cycle wherein the transistor 45 will again be rendered nonconducting.

It will accordingly be appreciated that with the above circuit that the controlled rectifiers 19 and 20 are inherently fast acting devices and thus current will flow therethrough abruptly. In order to substantially minimize the distortion in the output voltage wave caused by the abruptness of the change of the controlled rectifiers from a state of nonconduction to a state of conduction, the inductance 21, which has an impedance that is substantially more inductive than resistive is employed to cause the rate of change of current flow through the controlled rectifiers to be at a slower rate of increase thereby minimizing the distortion. With less distortion produced, it has been found that only filters 22 and 23 for filtering the third and fifth harmonics respectively of the alternating current source frequency from the output voltage wave are required to reduce the distortion in the output voltage to an acceptable minimum. If desired however, additional filters may be employed but each reduces the efiiciency of the regulator while reducing the distortion of the output wave.

It will accordingly be appreciated that there has been disclosed an automatic voltage regulator which produces a substantially constant output voltage with changes in the input voltage and/ or the power controlled by the regulator. The regulator employs relatively inexpensive parts and particularly employs semiconductor elements in a shunt path in the regulating unit. These elements are capable of reacting faster and of controlling larger current in the shunt path than have heretofore been found possible in other impedance devices. Moreover, in order to minimize the eifect of the semiconductor elements, the specific elements being disclosed being inherently only onoff devices, there is provided an inductive impedance in series therewith which under instantaneous conditions de creases the abruptness or acceleration of current flow sufiiciently to enable only a relatively few filters to be required in order to produce an output voltage which has an acceptable maximum distortion.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

I claim:

1. An automatic voltage regulator comprising a pair of input terminals connectible to a source of alternating current, a pair of output terminals connectible to a load and at which a desired value of voltage appears, autotransformer means having an intermediate tap connected to an input terminal and an end portion connected to an output terminal, a shunt path connected between the other end portion of the autotransformer means and the other input terminal and including semiconductor means, said semiconductor means including at least one controlled rectifier that is normally nonconducting but is rendered fully conducting upon receipt of a signal and inherently maintains itself fully conducting until the zero crossing of the current at the end of each half cycle and measuring means connected to sense the value of the output voltage and provide the signal to the semiconductor means at a point in each half cycle which causes the semiconductor means to be rendered fully conducting to produce the desired output voltage.

2. The invention as defined in claim 1 in which the shunt path includes an inductive means connected in series between the controlled rectifier and the other end portion of the autotransformer for decreasing the acceleration of current conduction in the shunt path upon the controlled rectifier being rendered conducting.

3. The invention as defined in claim 2 in which there is provided a filter means connected across the end portions of the autotransformer for substantially filtering the third and fifth harmonics of the alternating current frequency from the output voltage.

4. An automatic voltage regulator comprising a pair of input terminals connectible to a source of alternating current, a pair of output terminals connectible to a load and at which a desired value of voltage appears, autotransformer means having an input and an output, a shunt path connected in series with the input of the autotransformer means across the input terminals, said shunt path including semiconductor means and means for rendering said semiconductor means conductible upon receipt of a signal, said autotransformer means output being connected to said output terminals, and measuring means for providing a signal to the semiconductor means to vary the conduction of the semiconductor means to produce the desired output voltage, said measuring means including sensing means operatively associated with the output terminals for sensing the value of the output voltage and for supplying the signal to cause greater conduction of the semiconductor means when the output voltage value is lower than the desired value and lesser conduction of the semiconductor means when the output voltage value is higher than the desired value.

5. The invention as defined in claim 4 in which the sensing means includes a Wheatstone bridge having in one arm a photoconductive cell, a source of illumination mounted to direct illumination on said cell and means connecting the source of illumination to the output voltage to have the value of the illumination from the source of illumination vary in relationship to the value of the output voltage.

References Cited UNITED STATES PATENTS 3,281,654 10/1966 Reinert 323- 3,281,652 10/1966 Perrins 323-47 3,201,683 8/1965 Hjermstad et a1 323--22 JOHN F. COUCH, Primary Examiner. WARREN E. RAY, Examiner.

M. L. WACHTELL, H. HUBERFELD,

Assistant Examiners. 

